The present invention relates to a process cartridge (hereinafter called cartridge) of an image forming apparatus.
In an image forming apparatus, a cartridge which comprises integrated components such as a charging unit, a developing unit, a toner box, and a cleaning unit when necessary are installed around an image forming unit and can be installed in or removed from the image forming apparatus is often recently used.
FIGS. 8 and 9 show configuration examples. In FIG. 8, numeral 100 indicates a cartridge, and four components of an image forming drum 1, a charging unit 2, a developing unit 3, and a cleaner 4 are integrated. The cartridge can be installed in or removed from an image forming apparatus which is not shown in the figure, and the four units are relatively positioned and assembled in a housing 10 as specified.
Numeral 5 indicates a protective cover with a circular section for opening or closing an exposure opening 11 at the bottom of the image forming drum 1 which is installed at the bottom of the housing 10. A moving arm 13 which can freely rotate round a supporting point 12 installed on the side plate of the housing 10 is installed, the back end of the protective cover 5 is joined to and supported by a free end 14 of the arm 13 so that the back end can rotate freely, and a pin shaft 15 at the front end of the protective cover 5 is joined to and supported by a circular guide slot 16 of the side plate of the housing 10.
When the moving arm 13 rotates counterclockwise, the protective cover 5 moves to right and the exposure opening 11 at the bottom of the image forming unit (hereinafter called just the exposure opening) is opened. When the moving arm 13 moves clockwise, the exposure opening 11 is closed.
The protective cover 5 is used to prevent the image forming unit from being exposed to outside light through the exposure opening 11 when the cartridge 100 is removed from the image forming apparatus or to keep the image forming unit away from dust or damage due to contact with another object. The protective cover 5 may be designed so that it can be opened or closed manually or it is automatically opened or closed by a pin, spring, or cam when it is removed or installed.
Numeral 6 indicates a slit window for image exposure and 7 a shutter for opening or closing the window 6. The function of the shutter is the same as that of the protective cover 5.
When the cartridge 100 is installed in the image forming apparatus, the protective cover 5 and the shutter 7 are open. The surface of the image forming drum 1 exposed through the exposure opening 11 is opposite to a transfer unit 8 installed in the image forming apparatus.
When the pushbutton is pressed, the image forming drum 1 and a developing sleeve 3a start rotation in the directions of the arrows at a predetermined rotation speed and each unit is applied with a predetermined voltage. The image forming drum 1 is uniformly charged by the charging unit 2, and exposed to image exposure light L from an image exposure unit of the main unit of the image forming apparatus via the window 6. By doing this, an electrostatic latent image is formed on the image forming drum 1. The electrostatic latent image is subject to toner development by a developing unit 3b and transferred onto a recording paper P fed via the feed path from the feed unit of the main unit of the image forming apparatus by the transfer unit 8.
The recording paper with the toner image transferred on is separated from the surface of the image forming drum 1, fed to a fixing unit of the main unit of the image forming apparatus, fixed there, and ejected from the apparatus. The portion of the image forming drum 1 where the image transfer is finished is cleaned by scraping off residual toner with a cleaning blade 4a of the cleaner 4, charged by the charging unit 2 once again, and subject to the next image forming.
A developing unit 3 comprises a developing unit 3b and a toner box 3c. A developing sleeve 3a is installed in the developing unit 3b, and toner t is contained in the toner box 3c. The toner t in the toner box 3c is fed to the developing unit 3b via a through hole 3d to be used for development.
FIG. 9 is a drawing of another cartridge which is installed in a copier.
Numeral 17 indicates a document tray made of glass, which moves back and forth in the direction of the arrow during copy. The image on a document placed on the document tray 17 is irradiated with light from a document illuminating lamp 18 and rotated by a convergent light transmitter (trade name Selphox lens) 19 in the direction of the arrow in synchronization with the movement of the document. A latent image is formed on the image forming drum 1 with the entire surface charged by the charging unit 2 beforehand.
The electrostatic latent image is developed by the developing unit 3b. The recording paper P is fed by a paper feed roller 20 one by one, comes in contact with the image forming drum 1 via register rollers 21, transferred with the image on the image forming unit by the transfer unit 8, separated from the image forming drum 1 by a separation electrode 22, moves forward along a guide plate 23, and ejected outside the apparatus via fixing rollers 24 and paper ejection rollers 25. After image transfer, the surface of the image forming unit is eliminated residual charge by a discharging electrode 26 and removed residual toner by the cleaner 4, and then charged by the charging unit 2 once again to start the next image forming process. In this copier, the image forming charging unit 2, the developing unit 3, the transfer unit 8, the separation electrode 22, the discharging electrode 26, the cleaner 4, the illuminating lamp 18, and the guide plates 27, 28, and 29 are integrated to a cartridge 30 (indicated by an alternate long and short dash line), which is mounted so that it can be installed or removed by sliding on supporting rails 31 and 32 installed on the main unit. The cartridge 30 is locked at a predetermined location by a locking means, which is not shown in the figure, when it is used.
However, the following problems are imposed by the conventional cartridge configuration mentioned above.
The first problem, which is common to the cartridge configurations in FIGS. 8 and 9, is that the major components incorporated in the cartridge are installed around the image forming drum 1 only above the feed path for the recording paper P; that is, the charging unit 2, the developing unit 3b, the toner box 3c, and the cleaner 4 are concentrated around the image forming drum 1 only above the feed path for the recording paper P. Only the transfer unit 8 (the separation electrode in FIG. 9 is included) is under the paper feed path. For that reason, the dimensions of each unit are restricted. Although the dimensions may be changed, to increase the storage amount of toner, it is necessary to increase the capacity of the toner box or to make the toner box wider in consideration of a well-balanced shape.
The second problem is that since the recording paper feed path is under the image forming drum 1, the toner image on the image forming drum 1 is transferred onto the upper surface of the recording paper P. If the transferred image is fixed by the fixing rollers and the recorded paper is ejected as it is, the image surface is up. When a plurality of pages are printed by a printer sequentially starting at the first page, the pages are stacked in the reverse sequence with the first page at the bottom. If this occurs, it is necessary to rearrange the pages and it requires a great deal of time. To avoid it, it is necessary to turn over the recording paper once after fixing.
The third problem is that the transfer unit 8 and the guide plates 27 and 28 in FIG. 8 remain in the main unit of the apparatus, requiring a great deal of time for maintenance and inspection.
The fourth problem is that since the recording paper feed path in FIG. 9 cannot be revealed, it is rather difficult to clean the paper feed path or to remove jammed paper.